I had a mild head injury about 3 months ago. I went forehead first into a moving car and cut my forehead open. I went to the hospital to get it stitched up and woke up the next morning feeling fine. My head didnt hurt and I wasnt tired so I didnt think I had a concussion.

Last week I was sitting down and I got this intense smell of rotten eggs or sulphur for no reason at all and I got dizzy and felt like I was about to faint. I sat in the fresh air for a few minutes and it wore off. A friend was telling me its a long term concussion. I always thought concussions only lasted two days after the accident.

Could the smell of rotten eggs and the dizziness be a concussion 2 months after the accident?

It seems a little odd that you would experience a concussion 3 months after the accident. I do know that concussions can take a while to show. If I were you, I'd go to the doctor and get an MRI or CT scan of your head. Something doesn't sound right. Smelling odours that aren't there is something that should get checked out.
Hope you feel better.

Just as a person can have a visual hallucination or an auditory hallucination, you can also have an olfactory hallucination in which you truly believe as if you have smelt something that no one else is aware of. Roses, smoke, cigars...the eoisodes are usually not long lasting. Following a concusion it could be due to some residual swelling or what is known in young children as 'shaken baby syndrome'. The surface of the interior of the skull is not smooth like the exterior, it is jagged. During a concusion, and during your recent injury, the brain is jarred inside the skull and hits these inside jagged ridges. Are you noticing the rotten egg smell as a never ending experience, or did it come and then pass? I wouldn't be concerned unless hte episode was not ending, in which case I would then consult the doctor.